Which function fff satisfies f′′(x)+f(x)=0f''(x) + f(x) = 0f′′(x)+f(x)=0 with f(0)=0f(0)=0f(0)=0 and f′(0)=1f'(0)=1f′(0)=1?
sin(x)
cos(x)
e^x
sin(2x)